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3.
Assemble characters into words
4.
Assemble words into blocks
5.
Assemble blocks into messages
6.
Assign message routing
7.
Disassemble blocks into words for transmission
8.
Disassemble words into characters
9.
Put the character in the buffer for transmission.
The program to do this is divided into two basic cycles.
1.
Line service cycle (hardware scan and program scan) -- when each buffer is sampled
within a bit or character time and the bit or character present is moved to or from
the buffer.
2.
Processing cycle-- when all the rest of the processing to be done by the program
must.be accomplished. The bit buffer assembly areas and the other buffers are serviced
on a character time bases.
Since a basic premise of the DATANET-30 is to receive (or transmit) each bit or character
within rigid time limitations, the line service cycle must be initiated within a certain amount
of time.
Line Service
Line Service
+
Interrupt
+
171
Process
~171
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Scan
Hardware
Scan
Process
Program
Scan
The time will vary with the line service rate required by the remote terminals. One full cycle
must therefore be completed at a rate slightly faster than the fastest service rate. In order
to do this, processing must· be interrupted to allow the hardware scan instruction to service
the lines (3 word times per line).
The interruption must be timed so that, from the end of one
scan cycle to the end of the next scan cycle, the total elapsed time is less than one bit time.
Consideration must also be given to memory cycles used during the scan by the controller
selector peripherals.
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V-2
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